Various types of inking systems for offset printing machines have been proposed; in one construction, for example, the main ink roller is in continuous contact with the ink ductor roller. Other types of inking systems are known, for example systems in which the main ink roller is in engagement with the ductor roller only intermittently. Such systems have been described, for example, in M.A.N.-Druck-maschinen-Nachrichten, Issue 62, pp. 3 to 18, particularly FIGS. 6 and 14.
Continuous ink film supply systems have the disadvantage that if the printed subject matter is comparatively small, or small formats of paper have to be worked with, or the width of the printing material is small, the wetting liquid, typically water, from the fountain system will spread over essentially the entire width of the fountain system rollers and also in the region of those edge zones which will not have printed subject matter appear thereon. An excess of water will then occur in the inking system itself. This excess of water, particularly in the edge regions, will lead to a water-ink emulsion in which the proportion of water is excessive. This results in toning and other undesirable printing results and, further, decreases the viscosity of the ink so that the excessively water-saturated water-ink emulsion may splash or spray off the edges of rotating equipment. This difficulty may also arise in sheet printing machines.
Intermittently inked ductor inking systems have the disadvantage that the intermittent contact of the ink roller with the ductor roller results, necessarily, in transmission of a comparatively thick strip or band of ink to the ink roller. It may be difficult to spread the strip of ink uniformly over the final inking roller in engagement wth the plate cylinder, and it is difficult to reliably and securely provide for uniform surface inking, particularly if larger single-colored ink surfaces are to be printed at comparatively high machine operating speed. To uniformly spread such a strip of ink, it is necessary to provide a plurality of axially oscillating spreader rollers which increases the construction expense of the system. The larger number of spreader rollers is required to spread the ink film in a uniform layer over the final inking roller in engagement with the plate cylinder, for example. Many oscillating or other spreader rollers additionally interfere with flexibility of the apparatus since the reaction of the ink supply through the ink train to changes in the ink supply rate is slow.